Hi Todd,
Here are some examples from the 62nd and 98th sentais:
Ki-21-IIa 62nd Sentai, 1st Chutai
Ki-21-IIb 98th Sentai, 2nd Chutai
Ki-21-IIb 98th Sentai, 2nd Chutai
In case you don't know, the major versions of the Ki-21 were the Ki-21-Ia and Ki-21-Ib, which had "block" engine cowlings and the Ib had remote operated tail gun; the Ki-21-IIa and Ki-21-IIb, which had upgraded engines with more rounded streamlined cowlings and the IIb replaced the long dorsal "greenhouse" with a manually operated turret (as shown in the two examples of the 98th Sentai images). For some reason the second image shows a 98th Sentai ship with a dorsal turret and the long greenhouse. A mistake I believe but the camouflage depicted is still correct.
If you have a Facebook account I did a three part series of articles on the Ki-21 for SIG I am a member of. The articles have lots of pics, color plates and technical diagrams that may be of help to you. Here are the links:
Banzai Japanese Aviation Series - Mitsubishi Ki-21 - Sally in Betty's Shadow - Part 1 Design and Development
www.facebook.com/groups/1414345762215538/permalink/2302219300094842/
Banzai Japanese Aviation Series - Mitsubishi Ki-21 - Sally in Betty's Shadow - Part 2 Combat and Improvements
www.facebook.com/groups/1414345762215538/permalink/2303982449918527/
Banzai Japanese Aviation Series - Mitsubishi Ki-21 - Sally in Betty's Shadow - Part 3 Alternate Uses
and Successors
www.facebook.com/groups/1414345762215538/permalink/2306495399667232/
Hope this helps.